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SubjectRe: pre12 VM doubts and patch
On Wed, Sep 19, 2001 at 10:58:43PM -0700, Linus Torvalds wrote:
>
> On Thu, 20 Sep 2001, Andrea Arcangeli wrote:
> >
> > when the page is exclusive we definitely can write to it
>
> NO!
>
> If it is a read-only mapping, we must NOT mark it writable.
>
> The fact is, the page may have been written to earlier, marked read-only
> with mprotect(), and the page is dirty but read-only, and swapping it in

ah, I didn't thought at mprotect.

> MUST NOT markt it writable even if it is our last exclusive copy.
>
> Which we've gotten wrong for a long time, actually. But you #if 0'ed the
> fix that happened fairly recently.

hmm, the stuff inside #if 0 doesn't seem to be correct either there,
write_access doesn't mean we have the right to write to it, it just mean
we're trying to.

anyways here it is the fix:

--- 2.4.10pre12aa1/mm/memory.c.~1~ Thu Sep 20 07:20:03 2001
+++ 2.4.10pre12aa1/mm/memory.c Thu Sep 20 08:06:29 2001
@@ -1155,15 +1155,8 @@
pte = mk_pte(page, vma->vm_page_prot);

swap_free(entry);
- if (exclusive_swap_page(page)) {
-#if 0
- if (write_access)
- pte = pte_mkwrite(pte_mkdirty(pte));
-#else
+ if (exclusive_swap_page(page))
delete_from_swap_cache_nolock(page);
- pte = pte_mkwrite(pte_mkdirty(pte));
-#endif
- }
UnlockPage(page);

flush_page_to_ram(page);
thanks,
Andrea
-
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